York ZR Series Installation Manual

Also see for ZR SERIES: Technical guide Wiring diagrams Installation manual

Contents

275864-YIM-F-021346 Johnson Controls Unitary ProductsFigure 25: System Piping SchematicElectric Heating Sequence Of OperationsThe following sequence describes the operation of the electricheat section.Single-stage heating: (applies only to 18 KW heater, all otherheaters MUST use a two-stage thermostat)a. Upon a call for heat by the thermostat, the heatercontactor (6M) will be energized. After completing thespecified fan on delay for heating, the UCB will energizethe blower motor.b The thermostat will cycle the electric heat to satisfy theheating requirements of the conditioned space.Two-stage heating: (applies to all heaters except 18 KW)a. Upon a call for first-stage heat by the thermostat, theheater contactor (6M) (6M & 7M on 72 KW, 240V) will beenergized. After completing the specified fan on delay forheating, the UCB will energize the blower motor.If the second stage of heat is required, heater contactor(7M) will be energized. Note that on the 54 KW, 240Vheater, heater contactors (7M & 8M) will be energized andon the 72 KW, 240V heater, heater contactors (8M & 9M)will be energized. After completing the specified fan ondelay for heating, the UCB will energize the blower motor.b The thermostat will cycle the electric heat to satisfy theheating requirements of the conditioned space.NOTE: All 240 & 480V heaters are provided with manual resetbackup protection limits. These will de-energize theheaters should the primary limit fail to open or thecontactors fail to open in a failure mode.C1TXVFSLPSHPSCondenserFanAir Flow Air FlowAir FlowHot Gas Re-HeatSolenoid ValveIndoor BlowerBleed Line to clearthe Hot Gas Coilwhen it is not in useEvaporatorCoil Hot GasCoilCompressorPiping TPiping TCheckValveCondenserCoilCheckValveSol 2Suction linebleedOpen inReheatOpen inCoolingHPS(Sol 3)Sol 1Refrigerant flow in reheat modeRefrigerant flow in cooling modeAccumulatorFor units with VFD and electric heat, the speed of theindoor blower motor continues to be controlled by ductstatic pressure via the VAV control board.If there are VAV boxes present in the duct system, theboxes must be driven to the full-open position using acustomer-supplied power source to assure adequateairflow across the heating elements.